Rebel groups in the eastern Democratic Republic of Congo (DRC) arbitrarily executed at least 264 civilians, including 83 children, over a five-month period this year, according to report by United Nations human rights investigators, released today.

Many victims were hacked to death with machetes while others were burnt alive in their homes during more than 75 rebel attacks on villages in southern Masisi Territory, located in north-eastern DRC's North Kivu province, the report notes, according to a joint news release from the UN Joint Human Rights Office (UNJHRO).

"Investigators found that the victims were often those least able to flee the attacks, largely children and the elderly," added UNJHRO, which was established in February 2008, and comprises the Human Rights Division of the UN Stabilization Mission in the DRC (MONUSCO) and the local operation of the Office of the UN High Commissioner for Human Rights.

The investigators conducted more than 160 interviews with victims and witnesses during six missions - their findings have led to calls for action from the head of MONUSCO and the UN human rights chief.

In the news release, UNJHRO also warned that the actual number of atrocities could be "considerably greater" because security restraints prevented the investigators from being able to confirm "many more" reports of human rights violations.

"The figures noted in the report reflect cases documented in only some parts of Masisi over a relatively limited period of time, and are thus far from presenting a comprehensive overview of the human rights situation throughout eastern DRC," it said in the news release.

Violence has long plagued the area, particularly the provinces of North and South Kivu, where armed groups - some predominantly made up of one or another of the regions' various ethnic groups - have systematically targeted the civilian population, while also combating the DRC army, itself weakened by desertions this year.

"The ethnic dimension of the attacks is of particular concern in eastern DRC where tensions over the past 15 years, while fundamentally rooted in competition over land and natural resources, have resulted in cycles of violence committed along ethnic lines," UNJHRO said.

The investigation additionally conformed four cases of sexual violence involving the rape of 12 women. Other human rights violations outlined in the report include mass forced displacement and large-scale looting and destruction of private property.

Noting a "significant increase" in human rights violations throughout the Kivus this year, the Secretary-General's Special Representative for DRC and head of MONUSCO, Roger Meece, warned that the security situation could worsen.

"The risk of intensification of this ethnically charged conflict is real, and gives rise to serious concerns for peace and for the security of civilians in the region," he said.

The UN High Commissioner for Human Rights, Navi Pillay, called on the Congolese authorities to take immediate measures to protect civilian populations and to combat what she called "persistent impunity," which she said "only serves to embolden the killers."

"The systematic human rights violations committed by these armed groups, including the slaughter of so many children, are the most serious we have seen in recent times in the DRC," she added.

The human rights chief also said the UN was ready to offer support to DRC's recently launched judicial investigation into the atrocities, noting that these "must lead to the prosecution of those responsible for these acts and ensure justice for the victims."

In DRC, MONUSCO peacekeepers have been supporting DRC army deployments to the affected areas, including during the July-September period. The peacekeeping mission also sent several protection teams to Southern Masisi in order to evaluate the needs of the population and recommend action, which included establishing three temporary military bases and deploying 15 helicopter-supported foot patrols in the most volatile areas.

The UNJHRO investigators found that an armed group known as the Raia Mutomboki was responsible for most of the documented killings, while the opposing Nyatura group carried out others.

The report notes that the Raia Mutomboki was helped by allied community-based Mayi Mayi groups as it targeted mainly ethnic Hutus, a group that has long lived in eastern DRC, but whose numbers increased by the arrival of Rwandan Hutus in 1994 in the wake of power shifts that followed Rwanda's genocide that year.

The report goes on to note that the Nyatura group, sometimes in collaboration with the mFoundainly Hutu group known as the Democratic Forces for the Liberation of Rwanda (FDLR), mainly targeted people of Tembo ethnicity.

Many armed groups, according to the report, have stepped up their activities since the DRC army shifted its focus to pursuing a group of renegade soldiers who, after deserting this year, formed the 23 March Movement (M23) - a group whose own atrocities have been condemned by UN Secretary-General Ban Ki-moon and others in the international community.

"Important progress in tracking down the FDLR made early in 2012 by the Congolese army has been reversed since their redeployment to M23-threatened areas," UNJHRO said in the press release.

"Many armed groups," it added, "have taken advantage of the security vacuum left by the redeployment of army units to expand their own areas of influence, often carrying out violent attacks against civilians and exacerbating interethnic tension, already heightened by the M23."

AllAfrica publishes around 2,000 reports a day from more than 130 news organizations and over 200 other institutions and individuals, representing a diversity of positions on every topic. We publish news and views ranging from vigorous opponents of governments to government publications and spokespersons. Publishers named above each report are responsible for their own content, which AllAfrica does not have the legal right to edit or correct.

AllAfrica is a voice of, by and about Africa - aggregating, producing and distributing 2000 news and information items daily from over 130 African news organizations and our own reporters to an African and global public. We operate from Cape Town, Dakar, Lagos, Monrovia, Nairobi and Washington DC.